Hot computer security startup FireEye entered the public market on Friday with an IPO that raised over $300 million.

At the last minute, it raised its opening price more than $3, from a range of $15-$17 to $20. This let it raise far more than the $175 million it had hoped for in its original prospectus. Its open-day valuation is a healthy $2.3 billion, reports the New York Times Michael De La Merced.

The company became a startup to watch after it nabbed a bigwig as its CEO, Dave DeWalt, former CEO of antivirus software maker McAfee. It raised $85.5 million in investment from Sequoia Capital, Norwest Venture Partners, Juniper Networks, Silicon Valley Bank, the CIA's venture-capital arm, In-Q-Tel, and others.

FireEye's tech solves a really hard security problem. It can detect two types of hacker attacks that are very difficult to stop: "zero day" attacks and "advanced persistent threats."Zero-day attacks" are where hackers use bugs the software vendor hasn't yet fixed. The vendor has had "zero days" to come up with a fix. APTs are when hackers use all means possible to break into a particular network.

FireEye's security "appliance"— a combination of hardware and software — finds these attacks by running the suspicious code or opening suspicious emails in a protected area to see what they do. The process takes a fraction of a second.

The company has more than doubled revenue in the first half of 2013 to $61.6 million, from $29.7 million in the first half of 2012. It posted a net loss of $67.2 million for the first half, compared to a loss of $14.3 million in the same period of 2012.